The present invention relates to a magnetoresistive effect (MR) sensor using giant magnetoresistive effect (GMR) or tunneling magnetoresistive effect (TMR), to a thin-film magnetic head with the MR sensor, used for a magnetic recording and reproducing unit such as a HDD (Hard Disk Drive) unit or a FDD (Floppy Disk Drive) unit, to a manufacturing method of a MR sensor, and to a manufacturing method of a thin-film magnetic head.
Recently, a thin-film magnetic head with a MR sensor based on spin valve effect of GMR characteristics is proposed in order to satisfy the requirement for higher sensitivity and higher power in a magnetic head in accordance with ever increasing data storage densities in today""s HDD units. A spin valve effect (SV) MR sensor has a sandwich structure of first and second thin-film layers of a ferromagnetic material magnetically separated by a thin-film layer of non-magnetic material, and an adjacent layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer (pinned layer) to provide exchange bias magnetic field by exchange coupling at the interface of the layers. The magnetization direction in the pinned layer is constrained or maintained by the exchange coupling. On the other hand the magnetization direction of the first ferromagnetic layer (free layer) is free to rotate in response to an externally applied magnetic field. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magneto-resistance greatly changes and GMR characteristics are obtained.
The output characteristic of the SVMR sensor depends upon the angular difference of magnetization between the free and pinned ferromagnetic layers. The direction of the magnetization of the free layer is free to rotate in accordance with an external magnetic field from a magnetic medium. That of the pinned layer is fixed to a specific direction (pinned direction) by the exchange coupling between this layer and adjacently formed anti-ferromagnetic layer.
In this kind of SVMR sensor, an under layer is in general formed under the free layer. A material for this under layer will be selected so as to ensure (1) a high MR ratio by improving orientation in (1, 1, 1) plane of the free layer with a face-centered cubic structure, (2) a few diffusion into the free layer, and (3) an excellent corrosion resistance. More concretely, in case that the free layer has a multi-layered structure of a NiFe layer and a CoFe layer, the under layer is formed by Ta, Nb, Zr, Hf or else.
However, in case that the under layer is formed by such material, the improvement of the MR ratio is limited to 7-8% or less and a MR ratio of more than 10% cannot be expected even if the free layer material is appropriately selected.
In order to solve such problem, the assignee of this application has proposed, in a previous U.S. patent application Ser. No. 09/772,930 filed on Jan. 31, 2001 (now pending), a MR sensor which ensures a MR ratio more than 10% by forming an under layer having a face-centered cubic crystal structure and oriented in (1, 1, 1) plane.
Although a high MR ratio can be attained by using such under layer proposed in the previous patent application, a resistance change xcex94Rs of the MR sensor which corresponds to a final MR output cannot be increased. This is because diffusion into the free layer from this under layer is a little causing a relative resistance of the free layer to decrease and therefore a relative resistance of the whole multi-layered structure of the MR sensor to also decrease. As a result, it becomes difficult to narrow the MR sensor so as to satisfy the increased data storage density.
Furthermore, it is requested for a MR sensor with no under layer as formed in the MR sensor proposed in the previous patent application to improve variation in an asymmetry characteristics.
It is therefore an object of the present invention to provide a MR sensor with a great change in MR resistance xcex94Rs so as to conform to increased data storage density, a thin-film magnetic head with the MR sensor, a manufacturing method of the MR sensor, and a manufacturing method of the thin-film magnetic head.
Another object of the present invention is to provide a MR sensor that can improve variation in an asymmetry characteristics, a thin-film magnetic head with the MR sensor, a manufacturing method of the MR sensor, and a manufacturing method of the thin-film magnetic head.
The present invention concerns a MR sensor and a thin-film magnetic head with the MR sensor. The MR sensor includes at least one pinned layer, at least one nonmagnetic layer, and a free layer layered with the at least one pinned layer via the at least one nonmagnetic layer. A magnetization direction of the at least one pinned layer is fixed, and a magnetization direction of the free layer is variable depending upon a magnetic field applied to the free layer. A nonmagnetic metal is diffused in at least part of the free layer.
Since a nonmagnetic metal is diffused in a part of the free layer, a sheet resistance Rs of the free layer becomes large. In general, a resistance change xcex94Rs of the MR sensor is given from xcex94Rs (xcexa9)=MR (%)xc3x97Rs (xcexa9), where MR is a MR ratio and Rs is the sheet resistance. Therefore, if the sheet resistance Rs of the free layer increases, the change in MR resistance xcex94Rs increases. Thus, a high MR resistance change xcex94Rs above 2.5 xcexa9 can be obtained. Also, variation in asymmetry characteristics can be greatly improved. As a result, a narrower MR sensor to conform to increased data storage density and a thin-film magnetic head with the MR sensor can be obtained.
It is preferred that the sensor further includes a mutual diffusion layer made of the nonmagnetic metal and a metallic composition of the free layer is diffused in the mutual diffusion layer.
It is preferred that the mutual diffusion layer is inserted in the middle of the free layer, or that the mutual diffusion layer is layered on one face of the free layer and the other face of the free layer being in contact with the at least one nonmagnetic layer.
It is also preferred that the mutual diffusion layer has a thickness of 0.1 to 0.5 nm.
It is preferred that the nonmagnetic metal contains at least one component selected from a group of Al, Si, Ti, V, Cr, Mn, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Os, Ir and Pt.
It is further preferred that the sensor further includes at least one anti-ferromagnetic layer for fixing the magnetization direction of the at least one pinned layer using a bias magnetic field due to exchange coupling, the at least one anti-ferromagnetic layer being layered to contact with the at least one pinned layer. In this case, preferably, the at least one pinned layer has a single layer structure including a ferromagnetic layer, a multi-layered structure including ferromagnetic layers, or a multi-layered structure including ferromagnetic layers and a nonmagnetic layer.
It is preferred that the at least one pinned layer has a multi-layered structure including at least two ferromagnetic layers that are anti-ferromagnetically coupled with each other to have magnetic moments in opposite directions. Since the magnetization is automatically fixed, no anti-ferromagnetic layer for pinning by exchange coupling the pinned layer is needed.
It is also preferred that the at least one pinned layer is at least one ferromagnetic layer, a magnetization of the at least one ferromagnetic layer being fixed by a magnetic field produced due to a current flowing through the sensor. Since the magnetization is fixed by the bias magnetic field due to the sense current, no anti-ferromagnetic layer for pinning by exchange coupling the pinned layer is needed.
It is preferred that the at least one nonmagnetic layer consists of one nonmagnetic layer and the at least one pinned layer consists of one pinned layer, and that the sensor has a multi-layered structure of an under layer, the free layer, the one nonmagnetic layer and the one pinned layer sequentially layered in this order from a substrate side.
It is preferred that the at least one nonmagnetic layer consists of one nonmagnetic layer and the at least one pinned layer consists of one pinned layer, and that the sensor has a multi-layered structure of an under layer, the one pinned layer, the one nonmagnetic layer and the free layer sequentially layered in this order from a substrate side.
It is preferred that the at least one nonmagnetic layer consists of first and second nonmagnetic layers and the at least one pinned layer consists of first and second pinned layers, and that the sensor has a multi-layered structure of an under layer, the first pinned layer, the first nonmagnetic layer, the free layer, the second nonmagnetic layer and the second pinned layer sequentially layered in this order from a substrate side.
Preferably, the under layer is oriented in (1, 1, 1) plane.
Also, preferably, the sensor further includes a protection layer being oriented in (1, 1, 1) plane.
The present invention further concerns a method of manufacturing a MR sensor and a method of manufacturing a thin-film magnetic head with the MR sensor. The MR sensor is fabricated by sequentially layering at least one pinned layer with a magnetization direction fixed, at least one nonmagnetic layer and a free layer with a magnetization direction variable depending upon a magnetic field applied to the free layer. The method includes a step of forming a mutual diffusion layer substantially made of a nonmagnetic metal, and a step of diffusing the nonmagnetic metal in at least part of the free layer.
It is preferred that the forming step includes forming the mutual diffusion layer in the middle of the free layer, or forming the mutual diffusion layer on one face of the free layer, the other face of the free layer being in contact with the at least one nonmagnetic layer.
It is also preferred that the forming step includes forming the mutual diffusion layer with a thickness of 0.1 to 0.5 nm.
It is further preferred that the metal contains at least one component selected from a group of Al, Si, Ti, V, Cr, Mn, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Os, Ir and Pt.
It is preferred that the method further includes a step of forming at least one anti-ferromagnetic layer for fixing the magnetization direction of the at least one pinned layer using a bias magnetic field due to exchange coupling, the at least one anti-ferromagnetic layer being layered to contact with the at least one pinned layer. In this case, preferably, the at least one pinned layer has a single layer structure including a ferromagnetic layer, a multi-layered structure including ferromagnetic layers, or a multi-layered structure including ferromagnetic layers and a nonmagnetic layer.
It is preferred that the method further includes a step of forming the at least one pinned layer as a multi-layered structure including at least two ferromagnetic layers that are anti-ferromagnetically coupled with each other to have magnetic moments in opposite directions. Since the magnetization is automatically fixed, no anti-ferromagnetic layer for pinning by exchange coupling the pinned layer is needed.
It is also preferred that the method further includes a step of forming the at least one pinned layer as at least one ferromagnetic layer, a magnetization of the at least one ferromagnetic layer being fixed by a magnetic field produced due to a current flowing through the sensor. Since the magnetization is fixed by the bias magnetic field due to the sense current, no anti-ferromagnetic layer for pinning by exchange coupling the pinned layer is needed.
It is preferred that the method further includes a step of sequentially layering in this order from a substrate side, an under layer, a free layer with a magnetization direction variable depending upon a magnetic field applied to the free layer, a nonmagnetic layer and a pinned layer with a magnetization direction fixed.
It is preferred that the method further includes a step of sequentially layering in this order from a substrate side, an under layer, a pinned layer with a magnetization direction fixed, a nonmagnetic layer and a free layer with a magnetization direction variable depending upon a magnetic field applied to the free layer.
It is preferred that the method further includes a step of sequentially layering in this order from a substrate side, an under layer, a first pinned layer with a magnetization direction fixed, a first nonmagnetic layer, a free layer with a magnetization direction variable depending upon a magnetic field applied to the free layer, a second nonmagnetic layer and a second pinned layer with a magnetization direction fixed.
Preferably, the under layer is oriented in (1, 1, 1) plane.
Also, preferably, the method further includes a step of forming a protection layer oriented in (1, 1, 1) plane.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.